Shell construction
The shell-like structure is a characteristic of most celestial bodies - almost regardless of whether they are gaseous or solid .
Terrestrial planets have an internal structure which, like the structure of the earth, is divided into crust , mantle and core . The average density of each shell increases inwards. In the case of the earth, the typical density values are around 2.6 to 3 g / cm³ for the crust, 3–5 for the viscoplastic earth's mantle and over 10 for the largely liquid, highly ferrous core.
The nuclei of Mercury , Venus and Mars are - like those of the earth - also mainly made of iron , but in Venus and Mars somewhat smaller relative to the body as a whole, that of Mercury, on the other hand, is relatively larger.
The giant gas planets Jupiter , Saturn , Uranus and Neptune also have metallic cores, which can, however, also consist of highly compressed hydrogen . They make themselves noticeable to the outside through their magnetic field , as well as through the structure of the gravitational field .
The cause of the formation of shells in planetary bodies is the separation of their original substance through gravitational differentiation .
In the case of the sun and the fixed stars , the shell structure is characterized less by the chemical structure than by temperature , pressure and energy balance.